The warning came after two Iranian Su-25 fighter jets fired on an unarmed Predator drone conducting routine surveillance in international airspace east of Kuwait, 16 miles off the coast of Iran, Pentagon press secretary George Little told reporters Thursday following CNN's report.

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The drone was not hit, and it returned under its own power to its base, he said.

Little stopped short of calling the incident an act of war.

"I'm not going to get into legal labels. The reality is that we have a wide range of options, as I said before, to protect our assets and our forces in the region, and we'll do so when necessary," he said.

"The United States has communicated to the Iranians that we will continue to conduct surveillance flights over international waters, over the Arabian Gulf, consistent with longstanding practices and our commitment to the security of the region."

Little said the warning was delivered through Swiss diplomats who have acted on behalf of U.S. interests in Iran since Washington and Tehran cut ties in 1980.

"Our aircraft was never in Iranian airspace. It was always flying in international airspace. The recognized limit is 12 nautical miles off the coast, and we never entered the 12-nautical mile limit," he said.

The Obama administration did not disclose the incident before the presidential election.

Three senior officials confirmed the details to CNN on Thursday. The three spoke on condition of anonymity because of the sensitive intelligence nature of the matter.

Two of the officials said the fighter jets belonged to Iran's Revolutionary Guard Corps force, which has been more confrontational than regular Iranian military forces.

At least two bursts of gunfire came from the Su-25s' cannons, they said. The drone started to move away, but the Iranian aircraft chased it, doing aerial loops around it before breaking away and returning to Iran.

The drone's still and video cameras captured the incident, showing the two Su-25s approaching and firing their onboard guns, the officials said.

The Iranian pilots continued to fire shots that went beneath the Predator but never hit it, according to the officials.

U.S. military intelligence analysts are still not sure if the Iranian pilots simply were unable to hit the drone because of a lack of combat skill, or if they deliberately missed and didn't intend to bring it down.

But as one of the officials said, "It doesn't matter; they fired on us."

Little said the United States has to assume that Iran was trying to bring down the Predator.

Before Vahidi confirmed the action, another Iranian commander, Maj. Gen. Seyed Masoud Jazaeri, commented on the reports of the incident.

"The armed forces will respond decisively to any act of transgression," he said, according to the semi-official Fars News Agency.

"If any foreign planes try to enter our country's space, our armed forces will confront it," he was quoted as saying. "The defenders of the Islamic republic will give a decisive response to navy air, land or naval attacks."